1. Field of the Invention
The present invention relates to a key switch device, and more particularly to a key switch device having a structure capable of preventing its key top from being tilted, thereby maintaining the key top in a stable use state, while easily providing a desired waterproofing effect.
2. Description of the Related Art
Generally, portable electronic devices such as notobook computers use a keyboard including a plurality of key switch devices for a key input operation. Each key switch device includes a guide member consisting of a pair of links connected to each other in a crossing manner while being movable with respect to each other. The guide member has a function for guiding vertical movement of the key top to thereby effect a switching operation.
Such a key switch device is disclosed in a number of publications. An example of such a key switch device is disclosed in the Japanese Patent Publication No. 2924427 titled xe2x80x9cKEY SWITCH DEVICExe2x80x9d. Now, the structure of the key switch device disclosed in the publication will be described in brief with reference to FIG. 1.
The key switch device shown in FIG. 1 includes a key top 101 provided at a lower surface thereof with two mounting portions 102 and 103 vertically downwardly protruded from the lower surface of the key top 101, and a switching member 131 provided at its inner surface with a downward protrusion, and adapted to perform a switching operation in accordance with vertical movement of the key top 101. A support member 106 is arranged between the key top 101 and the switching member 131. The support member 106 includes two link members 107 and 108 connected to each other such that they are movable with respect to each other. Each of the link members 107 and 108 is provided at opposite ends thereof with mounting pins 115 and 121, respectively.
A flexible printed circuit board 130 is arranged beneath the switching member 131 while being supported by the upper surface of a support plate 125. Mounting pieces 135 and 136 corresponding to respective mounting portions 102 and 103 of the key top 101 are provided at the support plate 125.
The support plate 125 is made of a metal plate. The mounting pieces 135 and 136 are formed by cutting desired portions of the support plate 125, and then upwardly bending the cut portions. Accordingly, the mounting pieces 135 and 136 are integral with the support plate 125. The flexible printed circuit board 130 is provided with through holes (not shown) corresponding to respective mounting pieces 135 and 136.
The switching member 131 is made of a rubber material, so that it can serve to upwardly urges the key top 101 against a downward force applied to the key top 101 by its resilience.
In the conventional key switching device having the above mentioned configuration, the link members 107 and 108 move mutually in a scissors fashion when the user depresses the key top 101, thereby causing the key top 101 to move downwardly. When the depressing force is released, the key top returns to its original position by virtue of the resilience of the switching member 131. In the above procedure, the switching member 131 comes into contact with a contact on the flexible printed circuit board 130, thereby effecting a switching operation.
However, the above mentioned conventional key switch device has the following drawbacks.
First, there is a drawback in that it is difficult to machine the mounting pieces 135 and 136, to be engaged with the mounting pins 115 and 121, in a high accuracy because they should be integrally formed with the support plate 125, made of a metal, while having a structure protruded from the support plate 125. Accordingly, the support plate 125 is typically manufactured, using a relatively flexible metal material such as aluminum, in order to easily machine the mounting pieces 135 and 136 in a high accuracy. In this case, however, the mounting pieces 135 and 136 may be easily bent or broken, even when they are subjected to low pressure, because the strength of aluminum is low. Even when any one of the mounting pieces 135 and 136 is bent or broken, the support plate 125 cannot operate normally, so that it is necessary to replace the support plate 125 with a new one.
Where the support plate 125 is used for a keyboard including a plurality of key switch devices, it has a structure in which a plurality of mounting pieces 135 and 136 associated with the key switch devices are arranged in the form of a matrix. In this case, the formation of the mounting pieces 135 and 136 becomes more difficult in proportion to the number of the mounting pieces 135 and 136. As a result, it is difficult to manufacture the support plate 125.
Meanwhile, each key switch device included in a keyboard equipped in a notebook computer is required to have a structure in which its key top 101 is horizontally maintained at a constant level without being tilted, while having a long stroke.
In the above mentioned conventional key switch device, however, it is difficult to machine the mounting pieces 135 and 136 in the high accuracy required in the key switch device. Since the mounting pieces 135 and 136 are made of a flexible material such as aluminum, they may also be easily bent, tilt to one side thereof, or broken, even when they are subjected to low pressure. For this reason, the key top 101 may be tilted without being horizontally maintained.
Since the mounting pins 115 and 121 have a cylindrical shape, their area contacting the mounting pieces 135 and 136 and the support plate 125 is also small. As a result, the mounting pins 115 and 121 cannot stably support the key top 101. Furthermore, there is no structure for maintaining the key top 101 in a horizontal state. For this reason, it is impossible to prevent the key top 101 from being tilted.
In the above mentioned key switch device, its mounting pieces 135 and 136 are formed by cutting desired portions of the support plate 125, and bending the cut portions such that the cut portions are protruded from the support plate 125. As a result, holes are perforated through the support plate 125 at regions where the mounting pieces 135 and 136 are formed, respectively. For this reason-, there is a drawback in that it is necessary to attach a waterproofing tape to the lower surface of the support plate 125 or to otherwise close the holes, in order to waterproof the keyboard.
This results in an increase in the number of elements to be assembled and an increase in the number of assembly processes, thereby causing a degradation in productivity and an increase in manufacturing cost.
Also, in the conventional key switch device, the link members 107 and 108 are directly coupled to the mounting pieces 135 and 136 formed at the support plate 125, respectively. For this reason, the sliding movements of the link members 107 and 108 are limited by the height of the mounting pieces 135 and 136 formed by the cut portions of the support plate 125. Thus, the mounting pieces 135 and 136 serve as stoppers determining the height of the key switch device. In other words, the thickness of the support plate 125 determining the height of the keyboard corresponds to the thickness of the mounting plates 135 and 136. Accordingly, it is necessary to increase the thickness of the mounting plates 135 and 136 for a stable use state of the keyboard. In this case, however, there is a problem in that the height of the keyboard increases.
Therefore, the present invention has been made in view of the above mentioned problems, and an object of the invention is to provide a key switch device in which mounting pieces, to be engaged with mounting pins for guiding vertical movement of a key top, are formed, separately from a support plate adapted to support a printed circuit board, so that the support plate can be easily manufactured.
Another object of the invention is to provide a key switch device in which mounting pieces, to be engaged with mounting pins for guiding vertical movement of a key top, are formed, separately from a support plate adapted to support a printed circuit board, so that the key switch device has a firm structure.
Another object of the invention is to provide a key switch device capable of preventing its key top from being tilted, thereby providing a stable use state of the key top.
Another object of the invention is to provide a key switch device having a structure capable of providing a waterproofing effect without using a waterproofing tape or any other element, thereby reducing the number of elements to be assembled and the number of assembly processes, while achieving an improvement in the workability of the assembly process.
Another object of the invention is to provide a keyboard which has a reduced key height, so that it has a slim structure.
In accordance with one aspect, the present invention provides a key switch device comprising: inner and outer link members connected to each other in a crossing manner to mutually move in a scissors fashion, each of the inner and outer link members having support protrusions respectively provided in pairs at lower and upper ends thereof; a key top provided with receiving portions adapted to receive the support protrusions provided at respective upper ends of the inner and outer link members; a elastic switch provided at an inner surface thereof with a downward protrusion adapted to perform a switching operation in accordance with a vertical movement of the key top; a support plate arranged beneath the key top, and provided with cocking members at predetermined positions, respectively; a membrane arranged on the support plate, and printed with a circuit having a contact, with which the downward protrusion of the elastic switch comes into contact, and a switch pattern, the membrane having slots for allowing the cocking members to be upwardly protruded therethrough; and a mounting member arranged on the membrane, the mounting member having support pieces adapted to be engaged with respective support protrusions provided at the lower ends of the inner and outer link members, a central opening adapted to receive the elastic switch, and fitting holes adapted to allow the cocking members to be fitted therein.
Preferably, at least one of the support protrusion pairs provided at respective lower ends of the inner and outer link members has horizontal surfaces provided at respective support protrusions of the at least one support protrusion pairs, and adapted to come into contact with the support plate when the key top moves upwardly to a predetermined level, thereby stopping the upward movement of the key top. The support protrusions provided with the horizontal surfaces may be provided at the lower end of the outer link member.
The support protrusions provided at the lower end of the inner link member may have a cylindrical structure while being laterally movable during the scissors movements of the inner and outer link members.
Preferably, the inner link member is provided at a lower surface thereof with a support groove adapted to come into contact with one lateral end of the mounting member when the key top moves upwardly to the predetermined level, thereby vertically supporting the inner link member. The support groove may have an arc shape.
Preferably, the opening of the mounting member has a circular shape, and the mounting member has an annular frame formed around the circular opening while having a predetermined thickness.
The support pieces of the mounting member may be provided in pairs at front and rear ends of the mounting member, respectively, such that the support pieces included in the support piece pair provided at the front end of the mounting member are engaged with respective support protrusions provided at the lower end of the inner link member, whereas the support pieces included in the support piece pair provided at the rear end of the mounting member are engaged with respective support protrusions provided at the lower end of the outer link member. Each of the support pieces may have a 180xc2x0-rotated L shape.
Preferably, the mounting member is made of stainless steel.
Preferably, the fitting holes are arranged at opposite sides of the opening, respectively, such that they are symmetrical with respect to a center line of the opening. The mounting member may have recesses respectively formed around the fitting holes.
In accordance with another aspect, the present invention provides a method for manufacturing a key switch device, comprising the steps of: (A) cutting a plurality of first sheets respectively corresponding to the key switch devices to be manufactured, while having a predetermined strength, and forming support pieces, an opening, and fitting holes at each of the cut first sheets, thereby forming a plurality of mounting members respectively corresponding to the key switch devices; (B) cutting a second sheet to have a structure conforming to a shape required in a keyboard, and forming a plurality of cocking members at the cut second sheet, thereby forming a support plate; (C) preparing a membrane printed with a flexible switching circuit, and forming a plurality of slots, corresponding in number to the cocking members, at positions corresponding to those of the cocking members, respectively; (D) attaching the membrane to an upper surface of the support plate, positioning the mounting members on the membrane such that the cocking members are fitted in the coupling holes of the mounting members through the slots of the membrane, and protruded from the coupling holes at upper ends thereof, respectively, and applying a downward pressure to the protruded upper ends of the cocking members, thereby fixing the mounting members to the support plate; (E) arranging elastic switches in respective central openings of the mounting members fixed to the support plate; (F) preparing a plurality of linkages each including inner and outer link members connected to each other in a crossing manner to mutually move in a scissors fashion, each of the inner and outer link members having support protrusions provided at lower and upper ends thereof, and engaging the support protrusions provided at respective lower ends of the inner and outer-link members included in each of the linkages with the support pieces provided at an associated one of the mounting members, respectively; and (G) preparing a plurality of key tops each having receiving portions, and assembling the key tops to the linkages such that the support protrusions provided at respective upper ends of the inner and outer link members included in each of the linkages are received in and engaged with the receiving portions of an associated one of the key tops, respectively.
Preferably, the slots are formed, at the step (C), to have a size equal to or slightly larger than that of the cocking members.